The present invention pertains to carburetors and particularly to a carburetor capable of proportionately mixing an auxiliary fuel flow with a primary fuel flow to momentarily raise the fuel octane rating during those periods of engine operation when detonation is likely to occur.
The advantages of utilizing an auxiliary fuel for momentarily increasing an automotive fuel octane rating are set forth in U.S. Pat. No. 2,616,404. Such a concept is of particular interest in view of the use currently of unleaded fuels in automotive engines which have a compression ratio of about 8 to 1. This relatively low compression ratio is below the optimum ratio for most efficient engine operation but does enable acceptable knock-free engine operation throughout a range of operating conditions. Operation of an engine with a higher, more efficient compression ratio, say 9.5 to 1 or higher, would result in harmful detonation of the unleaded fuel particularly during periods of acceleration from low engine speeds.
The above noted patent discloses a fuel system wherein both intake manifold pressure and carburetor venturi pressure are utilized to control the merged flows of main and auxiliary fuels. While provision is made for combining the two flows prior to venturi discharge no consideration is given to the problem resulting from alcohol producing appreciably lower Btu's than a like amount of gasoline. In the prior art fuel system, valves on a common valve stem act to regulate main and auxiliary fuel flows into a nozzle serving passageway. The metering of main and auxiliary fuel flows is within a very limited range with no metering capability of increasing secondary enrichment and requisite Btu's to the fuel charge.
Other examples of dual fuel systems are found in U.S. Pat. Nos. 2,319,773; 3,805,756; 2,321,211; 4,085,720 and 4,090,484 which generically disclose carburetors with multiple fuel bowls, with manifold pressure responsive means controlling the fuel flows past a needle valve or similar valve device.
The use of alcohol as an anti-knock fuel additive is known as mentioned in earlier noted U.S. Pat. No. 2,616,404. Presently alcohol use in automobiles is, for the most part, as an extender termed gasohol wherein alcohol is limited to about ten percent of total fuel volume. Were such use of alcohol widely adopted it is doubtful if the benefits realized justify the increased cost to the consumer. Use of a greater proportion of alcohol is unsuitable in that the drop in the composite fuel Btu's is appreciable with a significant loss of power and poor engine performance.